Drying Lumber in the Attic

It's hot and dry up there maybe too dry. But for small amounts, attic drying is feasible, though tricky. December 1, 2005

I'm considering using my attic as a kiln for drying some 5/4 green walnut. It gets very hot up there (120+ deg.) and I live in a pretty dry climate at 7,000 ft elevation. Should I air dry some first? Should I set up a fan to blow over it? I'll end coat, of course, but I'm worried it'll dry too fast.

Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
I would also be worried, not because of the heat (which is typically about 40 F hotter than outside), but because of the very low RH.

From contributor D:
I've attic dried a few (small) loads here in OK. The key is to air dry the lumber to or below 20% MC first. Then sticker the lumber in the attic as you would outdoors. I never ran a fan over the lumber intentionally. We did run the indoor attic fan some. Dried white oak, 1-1/8" lumber, 20%. Attic drying is some work, but what ain't? Just don't overload!

From the original questioner:
Gene, what do you think about air drying first? Or could I humidify the attic somehow? What's the ideal RH?

From Gene Wengert, forum technical advisor:
You should air dry first. Humidifying the attic is not a good idea at all.

From contributor R:
Here's my experience with attic air drying. Instead of bringing the lumber to the heat, I set up a box and with fans and hoses, sucked the attic air to the lumber. Here is how it works successfully for me:

a. Lumber is air dried first.
b. Sticker lumber on hard surface (ground floor or 2nd floor of shop).
c. OSB sheathing makes for a cheap container - build around lumber to be dried.
d. Cut out holes for hoses (4" flex drains work) and install from lumber to peak of attic. Hoses equal number of fans, fans have been window insert type from Walmart-2 speed.
e. Hoses installed at top rear, fans located at bottom front, heated air simply collects moisture and passes through stack.
f. I hooked up a timer to the power of the fans. Set it to start at 10am and shut off at 8pm. Time can vary for a host of reasons.
g. Remember the moisture - it will stick to anything - insulation, sheetrock, etc. Make sure it gets out of harm's way.